The present invention relates to a safety steering column assembly for automobiles, in which a steering shaft of variable length is provided for connecting a steering wheel with a steering gear mechanism in which the steering shaft is surrounded at a portion adjacent the steering wheel by a guide and support tube. The guide and support tube, in turn, is surrounded by a corrugated impact absorption tube, in which the stiffness of the corrugations varies along the length of the latter and in which the corrugated tube abuts with one end at a fixed point of the body of the automobile.
Such a safety steering column assembly is known in the art and for instance disclosed in the U.S. Pat. No. 4,050,326. In this construction the guide and support tube is connected over a member with a predetermined breaking point to the body of the automobile. The guide and support tube is surrounded between the member with the predetermined breaking point and the end of the guide and support tube distant from the steering wheel by a corrugated impact absorption tube, which abuts with its end distant from the steering wheel against the body of the automobile. The end of the impact absorption tube adjacent the steering wheel is only spaced a small distance from the member with the predetermined breaking point. A connection between the guide and support tube with the impact absorption tube is not provided.
The impact absorption tube has corrugations which are of different stiffness on different axial sections thereof. A plurality of groups of corrugations are provided between the ends of the impact absorption tube and in each groups the corrugations have the same radial extension. The radial extension increases, however, from one to the next group. The impact absorption tube is mounted in stretched condition in the assembly and is therefore loaded in compressing during an impact.
During impact of the driver on the steering wheel the deformability of the impact pot arranged adjacent the steering wheel is first used. If thereby not sufficient impact energy is absorbed, the end face of the impact pot will abut against one end of the guide and support tube tending thereby to move the latter in axial direction against the resistance of the member with the predetermined breaking point. If the latter also breaks, the impact absorption tube is compressed by means of a bracket connected in the region of the aforementioned member with the guide and support tube after a short resistant-free axial movement of the bracket. During this compression the guide and support tube serves to prevent a lateral movement of the impact absorption tube.
The above-described safety steering column, as disclosed in the U.S. Pat. No. 4,050,326, avoids various disadvantages of other known safety steering columns since due to the different radial extension of the corrugations, a progressive increase of the resistance provided by the impact absorption tube is obtainable. However, it has been shown during the compression of the impact absorption member first corrugations with the greatest radial extension are completely compressed to a block before the next corrugation are likewise compressed to a block. From this will result a force-displacement diagram of sawtooth-shaped configuration in which the largest amplitudes are provided by the compressed corrugations having the smallest radial extension. The resistance provided by the impact absorption tube is therefore very irregular.
Among the many suggestions for the construction of safety steering columns there is also known a safety steering column with a corrugated impact absorption member in form of a sleeve in which the walls of the corrugations are arranged closely adjacent to each other and in which the upper end of the sleeve facing the steering wheel is fixedly connected to a portion of the body of the vehicle. (U.S. Pat. No. 3,475,984)
In this construction the corrugated sleeve is stretched upon impact. This has the advantage that upon impact the corrugated sleeve is more or less symmetrically stretched, under maximum possible consumption of impact energy without danger of clamping on the steering column, and without requirement of additional means to prevent such clamping.